Phylum Arthropoda

General Characteristics.

Arthropods contain jointed appendages that are modified in different species to carry out certain functions.

The exoskeleton is made of a mucopolysaccharide called chitin. As the animal grows it must get rid of the exoskeleton (molting) before a new one can form.

Arthropods contain well developed sense organs. Compound eyes, sensory antennae, and tympanic membranes keep most arthropods in communication with their environment.

An open circulatory system is found in all arthropods. The hemolymph (blood) is propelled through the body by a tubular heart and collected in areas called sinuses. These are very few blood vessels in the arthropods.

They contain a variety of respiratory organs such as book lungs, trachea, spiracles and gills.

They contain bilateral symmetry.

Most all arthropods reproduce sexually. Some species of insects are parthenogenetic. The female organism , under certain circumstances , can produce fertile offspring without mating. A complex developmental process is common in insects. This process is called metamorphosis.

They contain a ventral nerve cord and a brain.

Excretory organs vary from green glands to Malpighian tubules.

The digestive system is complex and very efficient.

They are protostomes and coelomates.

The phylum contain the most known species than all the other phyla combined.

Classes of Arthropods:

Crustacea. Lobsters, crayfish, crabs, and shrimp belong to this arthropod class. These organisms contain two body parts the cephalothorax and abdomen. Two compound eyes and two pairs of antennae. They contain appendages modified for grabbing and feeding. Their excretory organ consists of a sac-like green gland. Their gas exchange is through gills. Many species contain 5 pair of walking legs. The circulatory system is open. Barnacles are sessile crustaceans that have a modified exoskeleton in the form of a shell.

Insecta. This class contains the most prolific group of animals that has ever populated the earth. The exist in almost every environment known to man. Their ability to fly and live off of plants and flowers has given them this success. Insects contain three body parts: head, thorax, and abdomen. They contain one pair of antennae, a pair of compound eyes, and various modified mouth parts. The thorax contains the six legs and two pair of wings. They contain a well developed digestive system, and a ventral nerve cord. Their circulatory system is open and it contains a dorsal heart. They contain a tracheal respiratory system and excrete their liquid waste through Malpighian tubules. Many species young undergo complete, incomplete or gradual metamorphosis.

Arachnida. Spiders, ticks, mites, and scorpions contain simple eyes, two body parts the cephalothorax and the abdomen. They contain 4 pair of walking legs attached to the cephalothorax. Many breathe through book lungs. Many of these organisms are poisonous and parasitic.

Chilopoda and Diplopoda. These classes contain the centipede and millipede. Centipedes contain one pair of walking legs per segment and are carnivorous. The millipedes contain 2 pairs of walking legs per segment and are vegetarians.